get-config: WIP for #2: increase the retry to 7.

Also use the nice VARIABLE instead of hardcoding it.

7 retries takes around 2 minutes with curl exponential delays.

bin/get-config

 #!/bin/bash
 
 API_BASE_URL=https://labmanager-api.edu-al.unipmn.it/api/1.0
-MAX_RETRY=5
+# curl uses an increasing delay. 5 retries are tried in about 30 seconds,
+# so it's too quick for us. I increased it to 7, which is about 2 minutes.
+# Note: the same variable was also used in the `retry` function.
+MAX_RETRY=7
 RETRY_DELAY=5
 NORMAL_CONFIG_NAME=normale
 DEBUG=0
@@ -49,7 +52,7 @@ function debug() {
 # authenticate and get the token
 function getTokenJSON() {
     # store the whole response with the status at the end
-    HTTP_RESPONSE=$(curl --retry-all-errors --retry 5 -s -k -w "HTTPSTATUS:%{http_code}" --max-time 10 -X POST -H "Content-Type: application/json" -d "{\"login\":\"guest\",\"pwd\":\"\"}" ${API_BASE_URL}/login)
+    HTTP_RESPONSE=$(curl --retry-all-errors --retry ${MAX_RETRY} -s -k -w "HTTPSTATUS:%{http_code}" --max-time 10 -X POST -H "Content-Type: application/json" -d "{\"login\":\"guest\",\"pwd\":\"\"}" ${API_BASE_URL}/login)
     ret=$?
 
     if [[ $ret != 0 ]]; then
@@ -99,7 +102,7 @@ getConfigVars() {
     TOKEN=`echo ${TOKEN_JSON} | jsonValue token 1`
     MACHINE_NAME=`hostname`
     echo "Getting machine configuration..."
-    MACHINE_JSON=`/usr/bin/curl --retry-all-errors --retry 5 -s -k --max-time 10 -H "Authorization: Bearer ${TOKEN}" -X GET ${API_BASE_URL}/machines/name/${MACHINE_NAME}`
+    MACHINE_JSON=`/usr/bin/curl --retry-all-errors --retry ${MAX_RETRY} -s -k --max-time 10 -H "Authorization: Bearer ${TOKEN}" -X GET ${API_BASE_URL}/machines/name/${MACHINE_NAME}`
     MACHINE_ID=`echo $MACHINE_JSON | jsonValue id 1`
     MACHINE_CONFIGS_ID=`echo $MACHINE_JSON | jsonValue configs_id 1`
     CONFIG_NAME=`echo $MACHINE_JSON | jsonValue name 2`
@@ -125,7 +128,7 @@ getConfigFile() {
         echo "Error downloading config file (machine_id empty, maybe it is not in LabManager's DB)"
         return 1
     fi
-    HTTP_STATUS=`/usr/bin/curl --retry-all-errors --retry 5 -s -k -w "%{http_code}" -o /local/esame-machine.conf --max-time 10 --header "Authorization: Bearer ${TOKEN}" -X GET ${API_BASE_URL}/machines/${MACHINE_ID}/configfile`
+    HTTP_STATUS=`/usr/bin/curl --retry-all-errors --retry ${MAX_RETRY} -s -k -w "%{http_code}" -o /local/esame-machine.conf --max-time 10 --header "Authorization: Bearer ${TOKEN}" -X GET ${API_BASE_URL}/machines/${MACHINE_ID}/configfile`
     if [[ $HTTP_STATUS -ne 200 ]]
     then
         echo "Error downloading config file (http_status=$HTTP_STATUS)"
@@ -139,7 +142,7 @@ getConfigFile() {
 getIpConfigFile() {
     echo "Downloading machine iptables config file..."
     # get ipconfig file
-    HTTP_STATUS=`/usr/bin/curl --retry-all-errors --retry 5 -s -k -w "%{http_code}" -o /local/iptables --max-time 10 --header "Authorization: Bearer ${TOKEN}" -X GET ${API_BASE_URL}/machines/${MACHINE_ID}/ipconfigfile`
+    HTTP_STATUS=`/usr/bin/curl --retry-all-errors --retry ${MAX_RETRY} -s -k -w "%{http_code}" -o /local/iptables --max-time 10 --header "Authorization: Bearer ${TOKEN}" -X GET ${API_BASE_URL}/machines/${MACHINE_ID}/ipconfigfile`
     if [[ $HTTP_STATUS -ne 200 ]]
     then
         echo "Error downloading iptables config file (http_status=$HTTP_STATUS)"
@@ -152,7 +155,7 @@ getIpConfigFile() {
 
 updateCurrentConfigId() {
     # Update this machine's current config id
-    HTTP_STATUS=`/usr/bin/curl --retry-all-errors --retry 5 -s -k -w "%{http_code}" -o /dev/null --max-time 10 -H "Content-Type: application/json" -H "Authorization: Bearer ${TOKEN}" \
+    HTTP_STATUS=`/usr/bin/curl --retry-all-errors --retry ${MAX_RETRY} -s -k -w "%{http_code}" -o /dev/null --max-time 10 -H "Content-Type: application/json" -H "Authorization: Bearer ${TOKEN}" \
         -X PUT -d "{\"current_configs_id\":\"$MACHINE_CONFIGS_ID\"}" ${API_BASE_URL}/machines/${MACHINE_ID}/currentconfig`
 
     if [[ $HTTP_STATUS -ne 200 ]]